1. Field of the Invention
This invention relates to a colored article of aluminum or an aluminum alloy (hereinafter referred to collectively as "aluminum") and a method for the production thereof. More particularly, this invention relates to a method for imparting a fast and bright color to an anodic oxide film of aluminum by filling the pores in the oxide film to the deepest recesses thereof with a high-quality organic pigment or carbon black.
2. Description of the Prior Art
Heretofore, as means for effecting the coloration of an anodic oxide film of aluminum, numerous methods centering around the method of electrolytic coloring process using various metallic salts-containing baths and also including the methods of immersion coloration which use the bath containing inorganic compounds or the bath containing organic dyes have been known. The method of electrolytic coloring process, however, produces a desired color only with difficulty and, therefore, imposes a limit on the kinds of colors to be obtained. The dyeing methods, though capable of effecting coloration as required, entail the disadvantage that the colored oxide films obtained thereby are deficient in durability. It has been held that these conventional techniques encounter extreme difficulty in obtaining a brightly and primarily colored oxide film of such qualities as to fulfill various durability properties which facing materials for buildings are required to possess.
As measures to solve these problems, Japanese Patent Publication No. SHO 52-5010 proposes a method for effecting the coloration of aluminum by subjecting aluminum to anodic oxidation in an aqueous phosphoric acid solution and immersing the treated aluminum in a bath of fine dispersion of an aqueous pigment thereby inducing adsorption of the pigment onto a porous anodic oxide film formed on the surface of aluminum or a method which further coats the colored aluminum obtained as described above with a thermosetting resin. Japanese Patent Publication No. SHO 51-35177 proposes a method for attaining the coloration of aluminum by immersing aluminum which has undergone anodic oxidation in a nonionic or nonionic-cationic bath of a fine dispersion of an aqueous organic pigment and passing a direct current or an alternating current through the aluminum in the bath thereby inducing adsorption of the pigment onto a porous anodic oxide film formed on the surface of aluminum or a method which further coats the colored aluminum obtained as described above with a thermosetting resin.
These patent publications teach that the fine dispersion of the pigment having a particle size falling in the neighborhood of 1 .mu.m (1,000 nm), preferably not exceeding 0.5 .mu.m (500 nm) is used. In the aqueous pigment dispersion which is commercially available today, the pigment particles have an average particle diameter in the range approximately between 200 and 300 nm. On the other hand, in the anodic oxide film for which the aqueous pigment dispersion in used, the pores distributed therein generally have diameters of not more than 50 nm. Since most pigment particles are larger in diameter than the pores in the oxide film, therefore, the coloration of aluminum occurs in such a manner that the pigment is deposited by adsorption in the form of a layer at the mouths of the pores in the anodic oxide film and on the surface of the oxide film. The colored and pore-sealed aluminum of such a method, therefore, poses a problem of poor fastness of the imparted color to the impact of abrasion and consequent ready release of the pigment and, moreover, entails the disadvantage that fast coloration is not obtained unless the colored oxide film is coated with resin as disclosed in the patent publications mentioned above.